1. Midterm Winter 2002
Karl Lieberherr

2. CSU 670 has just been renamed from motivation:
Software Design and Development to
Advanced Pattern Matching and Brain Exercise
motivation:
software development will change, but
your pattern matching skills will be useful for the rest of your lives

3. Three-way pattern matching
Our brains are good at matching patterns
Given two instances of a pattern, find the correspondences between the instances and the pattern
pattern = class dictionary
instance 1: sentence
instance 2: object

4. pointcut X1(S s1) : this(s); sentence
AspectJFragment = <pointcuts> List(PointCut) EOF.
PointCut = "pointcut" PCName
<lhs> PCList(ArgDecl) ":" <rhs> PCExp ";".
PCName = Ident.
PCList(S) ~ "(" S { "," S } ")". List(S) ~ {S}.
ArgDecl = <t> Type Variable.
Type = Ident.
Variable = Ident.
class
dictionary
: AspectJFragment (
<pointcuts> : UNKNOWN-PARSE1 {
<first> : Nonempty_PointCut_List (
<it> : UNKNOWN-PARSE2 (
<pcname> : UNKNOWN-PARSE3 (
<ident> : Ident "UNKNOWN-PARSE4" )
<lhs> : ArgDecl_PCList {
<first> : Nonempty_ArgDecl_PCList (
<it> : UNKNOWN-PARSE5 (
<t> : UNKNOWN-PARSE6 (
<ident> : Ident "UNKNOWN-PARSE7" )
<variable> : UNKNOWN-PARSE8 (
<ident> : Ident "UNKNOWN-PARSE9" ) ) ) }
object

5. pointcut X1(S s1) : this(s); sentence
AspectJFragment = <pointcuts> List(PointCut) EOF.
PointCut = "pointcut" PCName
<lhs> PCList(ArgDecl) ":" <rhs> PCExp ";".
PCName = Ident.
PCList(S) ~ "(" S { "," S } ")". List(S) ~ {S}.
ArgDecl = <t> Type Variable.
Type = Ident.
Variable = Ident.
class
dictionary
: AspectJFragment (
<pointcuts> : UNKNOWN-PARSE1 {
<first> : Nonempty_PointCut_List (
<it> : UNKNOWN-PARSE2 (
<pcname> : UNKNOWN-PARSE3 (
<ident> : Ident "UNKNOWN-PARSE4" )
<lhs> : ArgDecl_PCList {
<first> : Nonempty_ArgDecl_PCList (
<it> : UNKNOWN-PARSE5 (
<t> : UNKNOWN-PARSE6 (
<ident> : Ident "UNKNOWN-PARSE7" )
<variable> : UNKNOWN-PARSE8 (
<ident> : Ident "UNKNOWN-PARSE9" ) ) ) }
establish
correspondence
object
establish
correspondence
using
colors

6. pointcut X1(S s1) : this(s); sentence
AspectJFragment = <pointcuts> List(PointCut) EOF.
PointCut = "pointcut" PCName
<lhs> PCList(ArgDecl) ":" <rhs> PCExp ";".
PCName = Ident.
PCList(S) ~ "(" S { "," S } ")". List(S) ~ {S}.
ArgDecl = <t> Type Variable.
Type = Ident.
Variable = Ident.
class
dictionary
: AspectJFragment (
<pointcuts> : UNKNOWN-PARSE1 {
<first> : Nonempty_PointCut_List (
<it> : UNKNOWN-PARSE2 (
<pcname> : UNKNOWN-PARSE3 (
<ident> : Ident "UNKNOWN-PARSE4" )
<lhs> : ArgDecl_PCList {
<first> : Nonempty_ArgDecl_PCList (
<it> : UNKNOWN-PARSE5 (
<t> : UNKNOWN-PARSE6 (
<ident> : Ident "UNKNOWN-PARSE7" )
<variable> : UNKNOWN-PARSE8 (
<ident> : Ident "UNKNOWN-PARSE9" ) ) ) }
establish
correspondence
object

7. For phases 3 and 4: List Structure
List(X)
first
X_List
NonEmpty_X_List
next it X

8. pointcut UNKNOWN-PRINT1 (A UNKNOWN-PRINT2, B UNKNOWN-PRINT3, C c3) :
sentence
PointCut = "pointcut" PCName
<lhs> PCList(ArgDecl) ":" <rhs> PCExp ";".
PCName = Ident.
PCList(S) ~ "(" S { "," S } ")".
ArgDecl = <t> Type Variable.
Type = Ident.
Variable = Ident.
class dictionary
<it> : PointCut (
<pcname> : PCName (
<ident> : Ident "X3" )
<lhs> : ArgDecl_PCList {
<first> : Nonempty_ArgDecl_PCList (
<it> : ArgDecl (
<t> : Type (
<ident> : Ident "A" )
<variable> : Variable (
<ident> : Ident "a1" ) )
<next> : Nonempty_ArgDecl_PCList (
object

9. Two-way pattern matching
Given a pattern and and a use of it, find correspondences between pattern and usage.
pattern = method
usage = inlined code

10. Iterator it = used.iterator();
while (it.hasNext()){
Variable curvar = (Variable) it.next();
System.out.println(); curvar.print(); }
java.util.Collection used
void
static UNKNOWN-ABS3 show(UNKNOWN-ABS4) {
UNKNOWN-ABS5
while (it.hasNext()){
UNKNOWN-ABS6
System.out.println(); curvar.print(); }
establish
correspondence
make method as general as possible! Who supports iterator()?

11. Two-way pattern matching
Given a pattern and and a use of it, find correspondences between pattern and usage.
pattern = a programming pattern
usage = an application in a specific context

12. DJ programming pattern:
AspectJFragment { {{
// method process finds all Compound-objects inside
// an AspectJFragment-object and prints the message:
// "This is a Compound expression: "
// for each Compound-object.
void process() {
UNKNOWN-AP1;
Main.cg.UNKNOWN-AP2(UNKNOWN-AP3, UNKNOWN-AP4, cV); } }}
CommandVisitor cV = new CommandVisitor();
this
"from AspectJFragment to Compound"
DJ programming pattern:
class-graph.traverse(what, where-to-go, what-to-do)
what = an object
where-to-go = a traversal strategy
what-to-do = a visitor

13. establish correspondence CommandVisitor { {{ // prints the message:
// "This is a Compound expression: "
// for each Compound-object.
void UNKNOWN-AP5(UNKNOWN-AP6){
System.out.println("This is a Compound expression: ");
host.print();
System.out.println(); } }}
Compound host
Selective visitor pattern:
Visitor { {{
void before (X host) { … use host … };
void after (X host) { … use host … }; }} }
establish
correspondence

14. Traversal strategy pattern: from A via X via Y to B
AspectJFragment { {{
// Find all Variable-objects on the left-hand-side
// (before the colon) of PointCut-objects
static String definedVarsSpec =
UNKNOWN-AP7
Answer:
from AspectJFragment via PointCut via -> *,lhs,* to Variable";
Traversal strategy pattern: from A via X via Y to B
AspectJFragment = <pointcuts> List(PointCut) EOF.
PointCut = "pointcut" PCName
<lhs> PCList(ArgDecl) ":" <rhs> PCExp ";".
PCName = Ident.
PCList(S) ~ "(" S { "," S } ")". List(S) ~ {S}.
ArgDecl = <t> Type Variable.
Type = Ident.
Variable = Ident.